The present invention relates to improvements in structures for forming a fibrous web from a suspension of fibers in a stock, and more particularly to a mechanism for preparing the stock and improving the dispersion and mixing of air in a surfactant foam and distributing the fibers throughout the foam. More basically, the invention relates to an improved mixing and dispersion device capable of improved ingestion of one fluid in another which is particularly well adapted and provides unique advantages in a foam generating system.
In the manufacture of fibrous webs, particularly from synthetic fibers, one method which has been developed involves suspending the fibers in a foam suspension. The system for one such arrangement is disclosed in U.S. Pat. No. 3,716,449.
In handling the foam generated by the process taught in the aforesaid patent, a requirement is that the foam not be permitted to break down so that the fibers are uniformly carried and uniformly distributed. To accomplish this the foam must be uniform and even uniform to the extent of having uniform bubble formation, and this can be accomplished by continual regeneration of the foam in its flow through the system toward the forming surface.
One very critical area when working with long synthetic fibers is that the location and the method employed for fiber addition. In a conventional paper machine, the wood fibers are added at the suction side of the fan pump, and the turbulence created by the pump disperses the fibers. On specialty grades, however, where longer than normal paper making fibers are utilized, this method cannot be used because the fibers would plug up the pump or become entangled with each other and with mechanical surfaces in the system. An important function of the mechanism is to obtain adequate and complete diffusion. This involves difficulty in machines that require different flow rates for different grades. A feature of the present invention is the provision of a mechanism which attains a unique result in that it provides structure which is capable of controlling the flow rate, which structure coacts to provide improved diffusion.
The diffusion mechanism of the invention may also be utilized as a mixer. Such mixers find use in the ingestion of dies and chemicals introduced into a liquid. Such mixing is utilized particularly in the paper industry, but also in the food processing and chemical industries. The ingestion, mixing and diffusion of fibers into a flowing liquid line is necessary wherein the fibers are picked up by water to be mixed in stock and is also necessary wherein the fibers are to be suspended in a surfactant foam rather than water. The features of the present invention may be employed in both types of systems.
It is an object of the present invention to provide an improved mixing and diffusion method and apparatus which employs the factors inherent in a flowing stream for the diffusion function by the structural relationship of parts.
A further object of the invention is to provide an improved diffusion and mixing apparatus which is particularly well adapted to the mixing and distribution of long fibers in a liquid in a paper making machine.
A further object of the invention is to provide an improved diffusion apparatus which functions for the continual regeneration of foam in a foam system suspending fibers in a surfactant foam.